Abstract

The legacy of industrial operations over the past 200 years are contaminated natural clays and clay-based sediments. There is an urgent need for economic methods to stabilize these materials since the problem is widespread. Chemical fixation or encapsulation of inorganic contaminants using lime provides one potential solution that has yet to be adequately explored.

This paper aims to review the methods of chemical stabilization of inorganic contaminants using pozzolanas, and in particular discuss the interaction of clays with both metal ions and lime. The parallels between cement, lime-fly ash and lime-clay stabilization reactions are examined to determine the potential for contaminant stabilization using lime and suggest the mechanisms upon which success would rely. The factors affecting the lime stabilization process are discussed. Methods of incorporation of lime in practice are thereafter discussed, covering deep mixing as well as surface mixing in situ and mixing ex situ. Specific research required to prove the potential of lime is then discussed.

The paper concludes that lime stabilization provides a potentially valuable and economic means of treating both natural clays and (often very wet) clay-rich sediments. This is achieved via both enhanced contaminant adsorption and precipitation of metal ions under conditions of high pH, and binding in of the contaminants with the reaction products of the pozzolanic reaction between lime and clay. However, the fundamental nature of the clay/sediment is altered by the lime-clay reactions, most notably in the context of future potential for ion mobility by an immediate increase followed by a progressive decrease in coefficient of permeability. The degree to which inorganic contaminants become associated with the reaction products and the permanency of this association under conditions of seepage (i.e. resistance to leaching) need to be researched in detail before confidence in the technique can be engendered.

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